58 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



was determined during a few hours. The results from these experi- 

 ments can, of course, not be taken as giving definite results as to 

 the use in respiration of the various sugars employed. First of all, 

 no account is taken of the possible conversion of the sugars in the 

 leaf during the time the sprouts were in the sugar solution. Also, 

 the length of time during which respiration determinations were 

 made was entirely too short to gain any conclusive idea as to the 

 true rate of this process, and it is very questionable whether it is 

 justifiable to draw conclusions as to the normal behavior of plants 

 from a study of etiblated shoots. Finally, Palladin carried out his 

 respiration determinations with levulose in diffuse light, which is 

 another disturbing factor. 



Such evidence as is now available seems to point to the conclusion 

 that in the plant, unlike the animal, d-levulose is not the most 

 easily oxidized sugar. Brown and Morris^ made comparative 

 analyses of the sugars in Troposolum majus. Two sets of excised 

 leaves were used; the one was analyzed immediately, the other 

 after having remained in the dark for 24 hours with the petioles 

 standing in water. Thus they found: 



Table 37. — Rate of emission of CO2 by 6 leaves of Helianihus annuus at 25°. 

 Petioles in nitrogen-free nutrient solution containing 7 per cent sucrose and 0.11 per cent 

 glycocoU. CO2 absorbed in Ba(0H)2 solution 0.11835 normal, 125 c. c. of which has the equiva- 

 lent of 0.3254 gram CO2. 



Evidently there is a considerable loss of carbohydrates due to 

 respiration, as well as a decided change in the relative amounts of 

 the various sugars. In all probability the starch was converted into 

 maltose, which yields dextrose, and the cane sugar was inverted to 



> Brown, H. T., and G. H. Morris. Jour. Chem. Soc. London, 63, 671 (1893). 



